total volume changes for the reactions are tdbu- uct was a hard insoluble phosphorus-containing lated, the time shown is the duration of illumina- polymer. Table 111 summarizes the results of oxidizing the tion until the incremental volume change was less than 1% in a half hour. The only generalization various phosphines with 96% nitric acid. In all which perhaps may be made is that the higher the cases but one, crystalline derivatives were prepared. ratio of phosphine to unsaturate, the faster the addi- I t was found that nitric acid oxidized the carbon tion reaction takes place. atom in the 3 position in 3-hydroxypropylphosphine In Table I1 the reactant proportions for the vari- to a carboxy group as well as oxidizing the phosous preparations and the products obtained to- phorus to a phosphonic acid group. However when gether with the elemental analyses are summarized. this phosphine was treated with 3 0 % ~ hydrogen . The experiments with isobutene and allyl chloride peroxide a t 100' only the phosphorus atom was are not included as no analytical data were ob- oxidized and 3-hydroxypropanephosphonic acid tained with the products of addition but only with was obtained. The titration curves obtained durthe oxidation products. The figures given for the ing the course of the equivalent weight determinayields of the various products should be construed tions gave further proof of the structures of the as indicating the order of the yields since handling acids as all phosphonic acids gave two end-points, losses were quite variable. The yield of 3-chl010- except 2-carboxyethanephosphonic acid which gave propylphosphine was low even though the coil- three, and all phosphinic acids gave one end-point, version of phosphine was 53%1, as thc iriain prod- EMBRYVILLE, CALII~UKXIA
[ COsTRII3crIOX
1;KOhl ?"E
UDREAU OF hlINE.5, PETROLEUM AND OIL-SHALE
EXPERIMENT STATION]
Thermal Decomposition of Sulfur Compounds. I. 2-Methyl-2-propanethiol BY C. J. THOMPSON, R. A. MEYERAND J. S. BALL' RECEIVED NOVEMBER 19, 1951 2-Methyl-2-propanethiol was thermally decomposed in a quartz tube utilizing a fiow method. The conditions (300-500 ' with exposure times of 10-120 seconds) employed in this study resulted in decompositions ranging from 0 to 97%. Thc predominant sulfur-containing decomposition product was hydrogen sulfide. In addition small amounts of elemental sulfur and residual sulfur were found. Isobutylene and isobutane were the major gaseous hydrocarbons produced. A frec radical chain type decomposition mechanism is proposed.
2-Methyl-2-propanethiol was decomposed in a quartz tube under various conditions of time and temperature. The temperatures employed were 300, 350, 400, 450 and 500°, with residence times of 10 to 120 seconds. These conditions resulted in decompositions ranging from 0 to 97%. The decomposition at temperatures above 500°, where secondary reactions become preponderant, was not studied. Satisfactory sulfur balances were obtained, and results were found to be reproducible. Hydrogen sulfide, elemental sulfur, and residual sulfur (compounds unreactive to ordinary reagents) were found as decomposition products in addition to the gaseous hydrocarbons, isobutylene and isobutane. The amount of decomposition increased with each rise in temperature and/or time of exposure. Based on experimcntal cvidence and supported by similar known reactions, a frec radical decomposition mechanism is proposed. Apparatus and Procedure Materials .-The
2-methyl-2-propancthiol was 99.92 iiiolc
yo purc, as determined by the freezing point method of
Kossini.2 All other reagents were C.r. grade or better. Apparatus.-The decompositions were made in a 25-mm.
0.d. quartz tube heated by a 3-unit Hevi Duty organic corn-
bustion furnace. The heated section of the furnace was 560 rnm. in length and contained a 27-mrn. i.d. copper tube which acted as a heat distribution jacket and also as a support for the reaction tube. The entire furnace was covered (1) To whom inquiries regarding this article should be sent (2) F. D. Rossini, A n d . Chrrn.. PO, 110 (1948).
with an asbestos blanket 3 mm. in thickness. Individual temperature control on each of the 3 furnace units was achieved by the use of a 3-point Celectray controller employing chromel-alumel thermocouples located in recesses in the copper tube. The thermocouples were protected from the direct heat of the furnace elements by thin pads of asbestos. The entire furnace and reaction tube were inclined at an angle of 7.5' from the horizontal. The sample was fed into the upper end of the decomposition tube by a positive feed mechanism. This feed device consisted of a hypodermic syringe and an eccentric and rachet drive, the shaft of which pushed on the plunger of the syringe. The hypodermic needle attached to the syringe was inserted into the reaction tube through a neoprene stopper. The speed of the motor, the number of teeth engaged per revolution, and the size of the syringe were all variable. Feed rate was, therefore, variable from 0.04 to 1.75 g./min. A 125-mm. section of the reaction tube extending from the lower end of the furnace was packed with glass wool. Two slanttube gas scrubbers (Fig. 1) were used in series at the exit end of the decomposition tube. These scrubbers each contained 100 ml. of 33% sodium hydroxide, which removed any hydrogen sulfide or thiol. This apparatus was designed to give complete gas scrubbing with very little back pressure. Test runs proved its ability to quantitatively remove hydrogen sulfide and thiol from the exit gases. Low-boiling hydrocarbons in the exit gases from the scrubbers were condensed in a trap cooled with a mixture of Dry Ice, carbon tetrachloride and chloroform. An A.S.T.M. Lamp Sulfur Apparatus, a Beckman Laboratory Model PH Meter, arid a Consolidated Model 21-102 Mass Spectrometer were also used. Procedure. (a) Temperature Calibration.-The temperature of the reaction tube was determined by a thermocouple placed equidistant from the walls of the tube. Readings were taken a t I-inch intervals and averaged to find the reported decomposition temperature. Temperature surge at any one point within the reaction tube was not greater . calibrations were made in an empty tube, than ~ t 1 . 5 ~All
July 5 , 1952
SUMMARY OF
tube gas scrubber.
but little temperature change was noted upon feeding the sample in a t the most rapid rate used. (b) Residence-Time Calibration.-This calibration was made with a special tube designed to have the same heated volume as the reaction tube, but wi;h a minimum volume between the end of the furnace and a trap filled with aqueous silver nitrate solution. Residence time was defined as the interval between the start of the feed and the discoloration of the silver nitrate due to reaction with the hydrogen sulfide and/or thiol as they reached the end of the furnace. Check runs were, in all cases, reproducible within 1%. (c) Decomposition Procedure.-After proper calibrations were made, the reaction tube, scrubbers, and cold trap were cleaned, reassembled, and swept with nitrogen for 5 minutes. A hypodermic syringe containing 10 to 15 ml. of 2-methyl-2-propanethiol was carefully weighed on an analytical balance and placed in the feed mechanism previously described. Eight to 10 ml. of the sample was then fed into the reaction tube a t the predetermined rate, and the hypodermic syringe was reweighed t o determine the exact quantity of sample added. The reaction tube, scrubbers and cold trap were then swept with nitrogen for 10 minutes. Analysis of Products.-(a) Products remaining in the reaction tube or caught by the glass wool plug were diluted with methyl ethyl ketone and benzene to an accurate volume. Suitable aliquots of this solution were then analyzed for total sulfur by the lamp method. Group sulfur analyses were carried out on other aliquots by the method of ~a11.3 ( b ) The liquid in the two slant-tube gas scrubbers was diluted to 1000 ml. and a suitable aliquot taken for potentiometric determination of hydrogen sulfide and thiol. The method used was that of Tamele, Ryland and Irvine' modified to include hydrogen sulfide determination. Hydrogen sulfide was precipitated at a considerably more negative potential, and there was a sharp break in cell e.m.f. between its precipitation and the precipitation of the thiols. Exhaustive testing proved this method to be both precise and accurate. Potentials were measured with Beckman Laboratory Model pH meter. (c) The low-temperature condensed material was analyzed in a Consolidated Model 21-102 Mass Spectrometer.
Results and Discussion Table I presents analytical data showing the effect of variation in time and temperature on the decomposition of 2-methyl-2-propanethiol. These data were obtained by the decomposition of the pure sulfur compound in a quartz tube. Studies on the pure material appear desirable, as dilution with hydrocarbons would complicate the analysis and influence the mode and extent of the decomposition. The quartz tube was used to minimize catalytic effects.
The material reported as residual sulfur was a red to black viscous liquid with a sulfur content of approximately 67y0. This material was found in increasing amounts as the severity of the cracking conditions was increased. From Table I curves were derived, Figs. 2 through 4, which show sulfur distribution as a func(3) J S Ball Bur Mcnes Rept Znue$ltgaitons, 3591 (1941) (4) M W Tamele. L B Ryland and V C Irvine, Ind Eng Chcm Anal E d , 13, 618 (1941)
TABLE I DECOMPOSITION EXPERIMENTS ON 8-hfETHYL2-PROPANETHIOL Residence --Per cent. sulfur as-Sulfur Free Resid- recovery, time, seconds R S H HIS S ual S %
'C.
Feed rate, g./min.
300 350 350 350 350 350 375 375 375 400 400 400 400 400 400 400 400 400 400 400 425 425 425 450 450 450 450 450 500 500 500
0.0674 120.00 93.1 1.6578 10.00 95.8 0.4102 30.00 95.0 .4142 29.71 97.8 .1724 60.00 86.7 .0502 120.00 23.8 ,4259 25.00 62.7 .2959 30.00 43.6 .1283 60.00 22.0 1.4885 10.00 92.6 1.5112 9.85 89.4 0.6757 20.00 63.7 ,4806 20.00 57.5 -4859 25.00 54.0 .4295 25.00 44.1 -3568 30.00 24.8 .3589 29.83 24.6 .2858 30.00 24.8 .1445 60.00 12.4 .1457 59.50 12.4 1.0946 10.00 60.6 0.8341 15.00 38.3 ,5232 20.00 17.8 1.2286 10.00 30.7 0.2846 30.00 8.1 .2849 29.97 8.0 .OS48 60.00 2 . 8 .OS61 59.13 2 . 1 1.1703 10.00 7.7 1.1761 9.95 10.2 0.2242 30.00 2 . 9
Temp.,
Fig. 1.-Slant
3285
OF 2-METHYL-2-PROPANETHIOL THERMAL DECOMPOSITION
0.0 0 . 0 0 . 0 .O .O 0.0 .O .O .6 .1 .O .4 .O .5 9.7 66.8 2 . 8 1 . 0 27.7 2.2 0.0 46.5 2 . 5 0 . 4 73.2 3 . 3 1.5 3.4 0 . 2 0.0 4.2 0 . 3 0.2 26.4 1 . 7 1 . 2 29.9 2 . 3 0 . 2 34.3 2 . 8 1 . 9 41.9 3 . 2 0 . 9 67.5 1 . 9 1.8 67.1 2 . 1 2.0 64.6 3 . 1 1 . 0 79.5 1 . 6 3 . 0 77.6 1.8 3.1 29.8 2 . 1 0 . 2 52.7 3 . 4 .6 72.3 4.0 .8 59.7 1 . 6 2 . 3 79.9 2 . 2 3.8 79.9 1.8 4 . 5 84.4 2.3 5 . 4 83.13.75.0 81.2 1.2 3 . 7 79.5 0 . 6 4 . 1 86.0 1.1 4 . 3
93.1 95.8 95.6 98.3 96.9 94.4 92.6 93.0 91.7 96.2 94.1 93.0 89.9 93.0 90.1 96.0 95.8 93.5 96.5 94.9 92.7 95.0 94.9 94.3 94.0 94.2 94.9 93.9 93.8 94.4 94.3
tion of residence time for the three temperatures. The values recorded on the graphs were obtained from the table after prorating the loss. Justification for this proration is readily evident in the two runs where no decomposition occurred. The reproducibility of the work can be observed
I
Residual Sulfur'
I
a
60
8 40
1 I
I
1
60
90
420
'Ot I
30
I
RESIDENCE TIME, SECONDS.
Fig. 2.-Effect
of residence time on sulfur distribution at 350'.
CI. J. THOMPSON, R. A. MEYERAND J. S. BALL
+ 11s. (CH3)2(CI-I,2)CSII+ (CII3)aCH (CHa)aCSH -tHS. +( C H ~ ) ~ ( C H ~ P ) C+S€I$ €I (CHI)~(CI-I.~)CSH +(CHa)*C=CHz + HS. (CII3)3CSH ---+ (CI-13)sC.
100
[CHJ),CSI-€
90 Residual Sulfur
u a
I
8 40
c
0
I
l
0
I
IO 30 60 RESIDENCE TIME, SECONDS
Fig. 3 --Effect of rriidciicr tirric 400’.
5‘r 6
mi
iulfur distribution
dt
+ (CH3)IC.--+
(Lij
(5)
(6) (7)
Reactions (5) and (6j produce the same free radical. As shown in reaction (7) it breaks down to give an HS. radical which may re-enter reaction (6) thus giving the chain-forming step. Analysis of the hydrocarbon gases shows a decrease in the butane/butene ratio as the reaction proceeds. This is in conformity with the proposed mechanism as reaction (5) producing isobutane is not a chain reaction while reactions (6) and (17) producing isobutylene are. The rapid increase in hydrogen sulfide forniation is also predicted by reactions (6) and (7). The mass spectrometer pattern for 2-methyl2-propanethiol (see Fig. 5) indicates that the carbon -sulfur bond is susceptible to cleavage. The high 57 peak observed is the parent peak less 33 and is indicative of the split into the two fragments (CH3)3Cand SH.
60 50 MASS TO CHARGE RATIO
40
Fig. 5.--hlass
1-
3 30 D
0
20 IO
0 0
60
30
IO
RESIDENCE TIME, SECONDS.
Fig. 4.--Effect
Vol. 74
of resitleiice time on sulfur distribution at
450
O.
by comparing, in Table I , runs obtained a t the same temperature and residence time. The data are in good agreement when proper allowance is made for the slight fluctuations in feed rate. Some of the runs were made after extensive furnace modifications. This work included rearrangement of the units and removal of four spacer plates, thus shortening the length of the heated section by 2 inches. Some variation in feed rate and deconiposition is reflected by these modifications. The products formed indicate that the over-all reactions are (CI-l:~)~~CSII (CII3)2C==CH2 -e--+
+ HzS
~ c I r , T ) ~ c zt.zILS - c ~+ ~ 2( C I M ~ C H+ s iCIH,)iC--Clil i- S --+ rcsidual sulfur
(I) (2) (3)
The rapid increase in rate of the reaction (Fig. 4)
and the formation of coinplex tarry products suggests the presence of a free radical mechanism such as that proposed by Malisoff and Marks.5 This mechanism for the reaction shown as (1) may be formulated ( 5 ) W. 51. LIalisoff a n d t.:. LT. M a r k s , I n d . E w . Chcm., 23, 1114 (1931) .
spcctra of 2-methyl-2-propanethiol
The “toluene carrier gas” technique6 for the detection of free radicals was employed in an attempt to prove the mechanism of decomposition. The conditions of temperature, pressure and flow rate were similar to those used in a normal decomposition run. Under these conditions secondary reactions became so troublesome that this technique proved to be unsatisfactory for establishing the reaction mechanism. If the pressure were decreased and the flow rate and dilution increased as suggested by the method, the initial decomposition temperature would be raised more than looo. Possibly the presence of free radicals could be detected a t the higher temperatures, but this would not prove the presence of free radicals during ordinary thermal decomposition a t the lower teniperatures. The decoinpositioii curve as shown in Fig. 2 suggests an induction period of some 60 seconds before the chain mechanism is contributing to an appreciable extent. At 400’ the induction period is inuch shorter and the decomposition is proceeding primarily by the chain reaction. At &go, Fig. 4, there is no measurable induction period with the decomposition being controlled almost entirely by the chain reaction. The low concentration of undecomposed thiol explains the leveling off of the curves in Figs. 3 and 4 a t residence times of 30 to 60 seconds. Reaction (2) can be written as a free radical mechanism, but this adds little to its understanding. It appears also to be reversed in some instances. (6) ?I Swarc C h r v z Krrsr
47, 7 i (IqiO)
JuIy 5, 1952
THERMAL DECOMPOSITION OF SULFUR COMPOUNDS : I-PENTANETHIOL
The effect of this reversal is shown graphically in Fig. 3, w h a e the elemental sulfur is seen to decrease between experiments a t 25 and 30 seconds residence time. Butafme/butene ratio measurements show a decrease of butane i n this region. The resultant effect of reaction (2) gives a maximum in the curve for the formation of elemental sulfur shown in Fig. 6. This is an effect seen only in a relatively narrow temperature range as experiments a t 375 and 425' showed almost no deviation from a smooth curve. Reaction (2) occurs to a very small extent a t lower temperatures because of the low concentration of elemental sulfur. At the higher temperatures, the reverse reaction appears to be very rapid. The reaction (3) of isobutene with elemental sulfur to give residual sulfur appears to follow closely the production of elemental sulfur. The product is probably a polysulfide material judging from the sulfur content. Acknowledgments.-This work was done under a cooperative agreement between the Bureau of Mines, United States Department of Interior, and
[CONTRIBUTION FROM THE
IO
30 4 0 50 60 70 80 THIOL DECOMPOSED, PERCENT
20
3287
90 100
Fig. 6.-Elemental sulfur resulting from thiol decomposition a t temperatures of 350, 400 and 450'.
the University of Wyoming. The authors wish to express their appreciation to the American Petroleum Institute, Research Project 48A, for the sample of 2-methyl-2-propanethiol used in this investiga tion. LARAMIE, WYOMING
BUREAUO F MINES,PETROLEUM
AND OIL-SHALE
EXPERIMENTAL STATION]
Thermal Decomposition of Sulfur Compounds. 11. 1-Pentanethiol BY C. J. THOMPSON, R. A. MEYERAND J. S. BALL' RECEIVED NOVEMBER 19, 1951 1-Pentanethiol was thermally decomposed in a quartz tube utilizing a flow method. The apparatus and techniques used in this investigation have been described in a previous publication. The conditions (350-500' with exposure times of 10 to 120 seconds) employed in this study resulted in decompositions ranging from 0.2 to 87%. The predominant sulfur-containing decomposition product was hydrogen sulfide. Small amounts of sulfides and residual sulfur were also produced. The decomposition, as postulated, proceeds by way of an intramolecular splitting of 1-pentanethiol to produce pentene and hydrogen sulfide.
Following the technique used by the authors2 in their thermal decomposition studies on 2-methyl-2propanethiol, 1-pentanethiol was decomposed under various conditions of time gnd temperature, The conditions employed in this study resulted in decompositions ranging from 0.2 to 87%. Satisfactory sulfur balances were obtained, and results were found to be reproducible. The predominant sulfur-containing decomposition product was hydrogen sulfide. Small amounts of sulfides and residual sulfur (compounds unreactive to ordinary reagents) were also produced. In addition, pentenes, butenes and other light hydrocarbons were found. Equations indicating some of the possible reactions involved in the decomposition are presented. Apparatus and Procedure
cracks between the upper and lower furnace sections with insulating cement, and the covering of the entire furnace with an asbestos blanket, 3 mm. in thickness. Except for these modifications, the furnace and feed mechanisms were the same in a previous investigation.2 A heated inlet system (Fig. 1) containing a loose glass-wool plug in the lower end, was used to volatilize the 1-pentanethiol before its entry into the decomposition tube. This preheating eliminated rapid volatilization of the sample within the reaction tube, thereby minimizing undesirable surge. A U-shaped tube containing 15 ml. of isooctane was attached to the lower end of the decomposition tube. A glass-wool gasdiffusion plug was held in the bottom of the outlet arm of the U-tube by means of several indentations in the tube. Exit gases from the U-tube were passed through a slant-tube gas scrubber containing 100 ml. of 33% sodium hydroxide. Low-boiling hydrocarbons in the exit gases from the scrubber were condensed in a trap cooled with a mixture of Dry Ice, carbon tetrachloride and chloroform. Procedure. (a) Temperature and Residence-Time Calibrations.-These calibrations were made by the methods used in a previous investigation.2 (b) Decomposition Procedure.-After proper calibrations Materials.-The 1-pentanethiol used in this investigation was 99.90 mole per cent. pure, as determined by the freez- for temperature and resistance time had been made, the reing-point method of Rossini.3 All other reagents were C.P. action tube, U-tube, scrubber and cold trap were cleaned, reassembled and swept with nitrogen for 5 minutes. A grade or better. Apparatus.-The decompositions were made in a 25-mm. hypodermic syringe containing 5 to 10 ml. of 1-pentanethiol 0.d. quartz combustion tube heated by a modified three- was carefully weighed on an analytical balance and placed unit Hevi Duty organic combustion furnace. Furnace in the feed mechanism. The sample was fed into the furmodifications included removal of the '/z" transite end plates nace a t the predetermined rate and the hypodermic syringe in all cases where two units came together, sealing of all reweighed to determine the exact weight of sample added. The entire system was then swept with nitrogen for 10 (1) T o whom inquiries regarding this article should be sent. minutes. ( 2 ) C. J. Thompson, R . A. Meyer and J. S. Ball, THISJ O U R N A L , 74, Analysis of Products (a).-Decomposition products re3284 (1952). maining in the reaction tube and the liquid in the U-tube (,'I) F. D.Rossini, A n d . Chcm., 20, 110 (1948). were composited and diluted to an accurate volume with
